1. Field of the Invention
The present invention relates to a broadband microstrip-waveguide transition apparatus having a broadband characteristic and operating in a millimeter waveband.
2. Discussion of Related Art
The ongoing development of high-speed, high-capacity wireless communication technology has driven up the operating frequency of wireless communication devices and the like to several tens of GHz and above, which corresponds to the millimeter wavelength region. In addition, the use environment is defined using the concept of a pico cell, which is a wireless communication system covering a small area, (that is, a short-range environment). In such an environment, a horn antenna, which has a higher antenna gain than a planar antenna when absorption in the atmosphere is taken into consideration, is mainly used at the outside of a transceiver module. Therefore, a microstrip-waveguide transition apparatus is required in order to transfer a signal from a radio frequency (RF) stage, in which the signal is transmitted in a plane such as a microstrip line, to a waveguide horn antenna.
According to research conducted thus far, an available frequency band of a transition apparatus that can be used in a frequency band of 60 GHz and above has a narrowband characteristic.
FIG. 1 is an exploded perspective view of a conventional microstrip-waveguide transition apparatus operating in a frequency band of several tens of GHz and above. As shown in FIG. 1, a conventional microstrip-waveguide transition apparatus 10 comprises a microstrip line assembly 12, a waveguide 14, and a ground plate 50 positioned between the microstrip line assembly 12 and the waveguide 14 and having an opening 52. The microstrip line assembly 12 includes a microstrip line 16 and a patch antenna 20. The microstrip line 16 includes a conductive ground plane 18 having a slot 22, a dielectric substrate 32 laminated on the conductive ground plane 18, and a strip conductor 30 that is positioned on the dielectric substrate 32. A portion 40 of the strip conductor 30 crosses the major axis of the slot 22 at a right angle. The patch antenna 20 includes a dielectric layer 34 and a conductor 38.
The conventional microstrip-waveguide transition apparatus 10 is formed so that the slot 22 perpendicular to the middle portion 40 of the strip conductor 30 and extending in the major axis direction is formed on the ground plane 18 of the microstrip line 16 to transfer a signal. The conductor 38 is formed on a lower surface of the dielectric layer 34 so that when the single patch antenna 20 resonates from the transferred signal the transferred signal propagates through the rectangular waveguide 14. However, since the conventional art uses a single patch antenna, it has a narrow resonance band characteristic, and thus is not appropriate for broadband communication.
In another conventional method, a microstrip line traverses a dielectric substrate without a slot, transfers a signal to a main patch antenna and a parasitic patch antenna both existing under the substrate, and propagates the transferred signal to a waveguide. However, since the main patch antenna and the parasitic patch antenna are formed on the same plane, this structure has a narrow resonance band characteristic.
Therefore, in order to widen the resonance band and enable use in broadband communication, a millimeter-wave band microstrip-waveguide transition apparatus having a new structure is required.